a) Field of the Invention
The present invention relates generally to a PCM(pulse code modulation) recorder which records a PCM signal along with a video signal by the use of rotary heads, and particularly to a recording system which is well suited to record a PCM signal on a tape after segmenting each field of the PCM signal.
b) Description of the Related Art
A system wherein a PCM audio signal is recorded along with a video signal by the use of rotary heads, is as disclosed in, for example, Japanese Patent Application Laid-open No. 31384/1990. Herein, each frame of the PCM audio signal is divided into five pieces, and each of the pieces is divided into two groups of even data items being the even-numbered data of the PCM audio signal and odd data items being the odd-numbered data thereof. The groups of even data items and odd data items are interleaved so that each frame is divided into a total of ten subframes for recording.
With this system, even when a dropout or a similar signal omission has occurred on a tape to render the reproduction of one subframe impossible, the audio signal is able to be reproduced by performing a mean value interpolation or the like from the preceding and succeeding data items. Further, it is contrived to shorten the recording/reproduction delay of the PCM audio signal relative to the video signal (AV delay). In an S-VHS VTR, accordingly, the system has become the basic format for recording the PCM signal in the deep-layer part of the tape.
Meanwhile, in an HD VTR which records the video signal of a so called "high vision" system of high definition, as illustrated in FIGS. 3(a) and 3(b), a rotary cylinder 34 on which two pairs of magnetic heads 30, 31 and 32, 33 are mounted in 180.degree. opposition is held faced to the surface of a magnetic tape 20 and is rotated at a frequency of 60 Hz being double the frame frequency of the NTSC system. Herein, a high-density recording is realized by forming record areas of 8 tracks per frame. The high-vision video signal and the PCM audio signal are subjected to timebase compression, and the resulting signals are respectively recorded in the corresponding areas 36 and 35 of the 8 tracks in time division. Those individual areas 37 of the area 35 in which the PCM audio signal is recorded, are referred to as "segments".
As regards the PCM audio signal of the HD VTR, in consideration of shortening a term for development and making circuitry common in a compatible set, it is thought advantageous that, as shown in FIG. 4, a signal processing circuit corresponding to the deep-layer recording PCM format of the S-VHS VTR can be utilized for recording the PCM audio signal of the HD VTR on the basis of the PCM format of the S-VHS VTR.
In the case of diverting the PCM format of the VTR of the S-VHS system to the PCM audio signal of the HD VTR, it should be noted that each frome of the PCM audio signal is divided into the ten subframes in the S-VHS VTR, whereas it is formed of the eight segments in the HD VTR, as mentioned above. Therefore, the PCM data divided by ten needs to be converted (rearranged) into the PCM data divided by eight.
It is important in the conversion to secure the capability of error corrections for the omissions of a reproduced signal attributed to dropouts etc. in the reproduction mode (i.e., the highest percentage of correctable data errors) and the capability of audio outputs (i.e., the reproduction of uncorrectable audio data as based on an interpolation), to simplify regulations in the conversion, and so forth.
By way of example, in a case where the interval between the even data and the corresponding odd data which arise within an identical time unit is short on the tape, the reproduction of temporally successive data items is rendered impossible even by a burst error of comparatively short duration. In addition to this, the processing of a mean value interpolation or the like fails to be performed.
With a scheme wherein the error correction is completed with a large number of tracks, there is the problem that, when a reproduction defect has occurred extending over one track, the error corrections of all the blocks becomes impossible.